1. Field of the Invention
The present invention relates to a molded resin laminate and a method for producing the same. Specifically, the present invention relates to a molded resin laminate which is excellent in dimensional accuracy and strength of a bent portion or a curved portion. The present invention also relates to a method for producing such a molded resin laminate.
2. Description of the Related Art
FIG. 10 shows a schematic vertical sectional view and a magnified view of major parts of a molded resin laminate concerning a conventional technique. The molded resin laminate 1 comprises a base layer 2, an intermediate layer 3, and a surface layer 4 which are joined to one another in this order. All of the respective layers 2 to 4 are made of resin materials. Among the above layers, the intermediate layer 3 is composed of a foamed resin component in which cells 5 having approximately equal diameters with each other are dispersed substantially uniformly.
The molded resin laminate 1 is produced as follows.
At first, an injection molding machine is subjected to the mold clamping, and then a molten resin (molten material) is injected into a cavity of the injection molding machine. The molten material is cooled and solidified, and thus a base resin component, which is composed of a molded resin piece, is prepared.
Subsequently, after the mold opening is performed, the base resin component is taken out and it is held on a first mold of a vacuum forming machine. In this state, an adhesive is applied to the surface of the base resin component.
Subsequently, a sheet-shaped laminate, which is composed of a foamed resin component and a resin cover joined to the foamed resin component, is arranged between the base resin component and a second mold of the vacuum forming machine so that the foamed resin component may be opposed to the base resin component. Then, the mold clamping is performed. As a result, the sheet-shaped laminate is coarsely bent and deformed along the shape of the mold.
Further, the gas in the cavity is vacuum-evacuated by the aid of the mold disposed on the side to make abutment against the sheet-shaped laminate so that the pressure in the cavity may be a negative one. Accordingly, the sheet-shaped laminate is allowed to make tight contact with the mold. Accordingly, the sheet-shaped laminate is finely bent and deformed along the shape of the mold, and a boarding or graining pattern is transferred to the surface layer. Thus, a bent section R (see FIG. 10) is formed which has a predetermined superficial shape and a bending ratio.
After the vacuum evacuation of the gas from the cavity is completed, the compressed gas is supplied to the cavity via passages previously formed in the mold with which the sheet-shaped laminate makes the tight contact, or the passages are allowed to be open to the atmospheric air, and the gas in the cavity is vacuum-evacuated via gas-aspirating holes which are previously formed in the base resin component and the mold with which the base resin component makes the tight contact respectively. Accordingly, the foamed resin component is directed to and pressed against the base resin component. Therefore, both of the foamed resin component and the base resin component are strongly joined to one another by the aid of the adhesive.
Finally, the mold opening is performed after completing the supply of the compressed gas to the cavity and the vacuum evacuation of the gas from the cavity. Thus, the molded resin laminate 1 is obtained which comprises the base layer 2 composed of the base resin component, the intermediate layer 3 composed of the foamed resin component, and the surface layer 4 composed of the resin cover. The base layer 2, the intermediate layer 3, and the surface layer 4 are joined to one another in this order.
The molded resin laminate 1 produced as described above is used as an instrument panel, a bumper of an automobile or the like.
In the method for producing the molded resin laminate concerning the above conventional technique, shrinkage cavity may appear at the bent section R of the molded resin laminate 1 or the strength of the bent section R may be unsatisfactory. The reason is that the ductility of the foamed resin component to be formed into the intermediate layer 3 is poor. Therefore, the foamed resin component 3a is insufficiently expanded and elongated as shown in FIG. 11 when the sheet-shaped laminate is allowed to make tight contact with the mold by giving the negative pressure in the cavity to form the bent section R. Further, since the resin cover 4a is joined to the foamed resin component 3a, the expansion and the elongation of the resin cover 4a are quite limited. The shrinkage cavity appears at the bent section R for this reason as well.
In FIG. 11, reference numeral 2a indicates the base resin component to be formed into the base layer 2. Reference numerals 6, 7 indicate a male mold and a female mold which are provided for the unillustrated vacuum forming machine. The cavity 8 is formed by clamping both of the molds 6, 7. Reference numerals 9, 10 indicate gas-aspirating holes formed in the male mold 6 and the female mold 7 respectively. Reference numeral 11 indicates holes which are formed in the base resin component 2a and which communicate with the gas-aspirating holes 9 of the male mold 6.
Because the foamed resin component 3a is expanded and elongated at the bent section R, the wall thickness of the foamed resin component 3a becomes thin thereat. The strength of the bent section R is consequently decreased as compared with that of flat portions. Furthermore, any crack 12 may appear since the cell 5 is extended, and the cells 5, 5 are deformed and connected to one another. Then, the strength of the bent section R is further decreased.
That is, the method for producing the molded resin laminate concerning the conventional technique involves a problem that it is impossible to produce, with a satisfactory yield, any molded resin laminate 1 which is excellent in dimensional accuracy and strength of the bent section.
On the other hand, Japanese Laid-Open Patent Publication No. 9-12762 discloses a foamed resin component in which the diameter of cells disposed at a central portion is larger than that of the cells disposed at a surface layer portion. According to the above patent document, when the foamed resin component is joined to a surface coating material composed of a resin material or a cloth at a high temperature, an irregularity does not occur in the foamed resin component. In a laminate thus obtained, an air does not invade the space between the surface coating material and the foamed resin component.
It is certain that detailed evaluation is made for a case in which the single foamed resin component is subjected to a vacuum forming process in the above patent document. However, no trial is made to perform a vacuum forming process for the surface coating material and the foamed resin component integrally. Therefore, no trial is made to suppress the occurrence of the shrinkage cavity on the surface coating material in this process as well.
That is, no technique has been hitherto established to suppress the occurrence of the shrinkage cavity on the surface layer 4 when the foamed resin component 3a and the resin cover 4a are integrally subjected to a vacuum forming process as described above.